Method for handling the shutdown of a turbomachine string in a liquefaction plant of a gaseous product

Abstract

A method for handling the shutdown of a turbomachine string installed in a plant for the liquefaction of a gaseous product comprising at least two turbomachine strings comprises the steps of detecting the shutdown of a first turbomachine string; promptly increasing the driving torque on a shaft of a second turbomachine string when the shutdown is detected; maintaining the driving torque increase on the shaft of the second turbomachine string until a preset speed of the motor driver is reached or a predetermined period of time expires.

What we claim is: 
     
       1. A method for handling a shutdown of a turbomachine string, the turbomachine string being installed in a plant for a liquefaction process of a gaseous product, the plant comprising a first turbomachine string and a second turbomachine string, the method comprising the steps of:
 detecting a shutdown of the first turbomachine string caused by a shutdown event associated with the first turbomachine string, the first turbomachine string including at least one first motor driver and at least one first driven compressor; 
 increasing a driving torque on a shaft of the second turbomachine string when the shutdown is detected, the second turbomachine string including at least one second motor driver and at least one second driven compressor; and 
 maintaining the driving torque increase on the shaft of the second turbomachine string so that a speed of the at least one second motor driver is increased from a current speed to a preset speed for a predetermined period of time from when the shutdown was detected, 
 wherein the driving torque increase is obtained through setting a driving torque request value of the at least one second motor driver of the second turbomachine string during the shutdown event associated with the first turbomachine string, said driving torque request value being higher than a preset driving torque request of the at least one second motor driver during a normal operating condition, and 
 wherein the driving torque increase occurs before an anticipated higher load acts on the second turbomachine string and is not simply a reaction to dynamics of the second turbomachine string. 
 
     
     
       2. The method according to  claim 1 , wherein the at least one first motor driver and/or the at least one second motor driver is a turbine, a helper motor, or an electric helper motor. 
     
     
       3. The method according to  claim 1 , wherein the preset speed is a maximum operating speed of the at least one second motor driver. 
     
     
       4. The method according to  claim 1 , further comprising the step of maintaining the preset speed for the predetermined period of time or until the shutdown event associated with the first turbomachine string is ended. 
     
     
       5. The method according to  claim 1 , further comprising the step of maintaining said driving torque increase until the shutdown event associated with the first turbomachine string is ended. 
     
     
       6. The method according to  claim 1 , wherein the driving torque request value of the at least one second motor driver is obtained as a function of the current rotation speed of the shaft of the second turbomachine string and of a current driving torque request value. 
     
     
       7. The method according to  claim 1 , wherein the driving torque request value of the at least one second motor driver is obtained as a function of a target rotation speed of a turbine attached to the shaft of the second turbomachine string. 
     
     
       8. The method according to  claim 7 , wherein the target rotation speed of the turbine is obtained as a function of the current rotation speed of the shaft. 
     
     
       9. A control unit for a motor driver of a turbomachine string, the control unit comprising:
 a sensor module configured to detect a speed of a shaft of a first turbomachine string including a first motor driver; 
 a torque setting module configured for setting a torque of the first motor driver; and 
 a detection module operatively connected to the torque setting module, the detection module configured to detect a shutdown of a second turbomachine string, 
 wherein the torque setting module is configured to promptly increase a driving torque on the shaft of the first turbomachine string when the shutdown is detected and to maintain the driving torque increase on the shaft of the first turbomachine string so that a speed of the first motor driver is increased following detection of the shutdown from a current speed to a preset speed for a predetermined period of time from when the shutdown was detected, 
 wherein the torque setting module comprises an operating module configured to set a driving torque request value of a helper motor of the first turbomachine string during the shutdown of the second turbomachine string, the driving torque request value being higher than a preset driving torque request of the helper motor during a stationary operating condition, and 
 wherein the driving torque increase occurs before an anticipated higher load acts on the second turbomachine string and is not simply a reaction to dynamics of the second turbomachine string. 
 
     
     
       10. The control unit according to  claim 9 , wherein the torque setting module comprises an operating module configured to compute a driving torque request value of the helper motor as a function of a current rotation speed of the shaft of the second turbomachine string and of the current driving torque request value. 
     
     
       11. The control unit according to  claim 10 , wherein the operating module is configured to compute the driving torque request value of the first motor driver as a function of a target rotation speed of a turbine attached to the shaft of the second turbomachine string. 
     
     
       12. The control unit according to  claim 11 , wherein the torque setting module comprises a turbine speed setting module configured to compute the target rotation speed of the turbine as a function of a current rotation speed of the shaft. 
     
     
       13. A turbomachine string comprising the control unit according to  claim 9 .